Scientists are working hard to find new ways to defeat bacteria that are increasingly resisting the antibiotics already available.

These range from continuing to develop new antibiotics to keep up with bacteria's rapid evolution to giving bacteria themselves disease - bugs are, like larger organisms, susceptible to viruses.

Since the introduction of penicillin bacteria have been proving themselves ever more adept at defeating antibiotics - soon after its introduction in the 1940s resistant strains of bacteria began to appear.

The response has always been to develop new classes of antibiotics that can tackle the resistant strains, and until recently doctors were well ahead of the game.

But with the emergence of bacteria resistant to even the most powerful antibiotics, scientists are having to look at other approaches.

Localised use

That is not to say scientists have given up on new drugs - a team in Seattle are working on a new type of antibiotic cream to treat foot ulcers.

Early studies show it is just as effective as antibiotic pills usually used to treat the condition, but the researchers say it combats resistance because it is applied only where it is needed.

Overuse of antibiotics is the main cause of resistance, and the nature of a cream application will mean there is less opportunity for this to happen.

However, this in itself will not prevent bacteria gaining resistance - it will simply take longer to happen.

Adapting to change

Researchers at the University of Limerick are taking another approach, and working against the very characteristics that make a bacterium resistant.

Resistance occurs partly because bacteria reproduce so quickly - one bacterium with a mutation can survive the antibiotic and reproduce millions more with the same resistance within the space of a day.

The Limerick scientists think they have found a way to adapt the antibiotic so that it recognises the mutant bacteria and destroys them before they reproduce.

They say some bacteria are able to negate penicillin's infection-fighting properties by producing enzymes that cut out a critical part of the penicillin molecule.

The team has produced a prototype penicillin structure that works by incorporating a unique fragment to the penicillin molecule, which is fatal to bacteria and specifically activated only when a bacterium attempts to change the drug's molecular structure.

Diseased bugs

But the ultimate answer may lie outside antibiotics with an idea that first appeared before the First World War but was abandoned after the recognition of penicillin's power in 1943.

It involves exploiting bacteria's natural enemy - viruses known as bacteriophages, which enter the bacterium and kill them. They have proven more effective than antibiotics in some animal studies.

Work in the former Soviet Republic of Georgia and the UK is looking at how to exploit them in treating infected humans.

However, bacteriophages are extremely specific and have to be matched to exact strains of bacteria, meaning that an infection that kills rapidly could not be treated quickly enough.

The ultimate superdrug - that can kill all known germs without killing their human host - is still a long way off, and, given the remarkable power of bacteria to evolve, its supremacy would most likely be short lived.